In recent years, a greenhouse effect caused by CO2 has been pointed out as one of causes of global warming. Accordingly, measures against the greenhouse effect have been urgently and internationally needed for the protection of the global environment. Since a source of CO2 corresponds to the whole field of human activity using the combustion of fossil fuel, a demand for the suppression of CO2 emission tends to become stronger. Accordingly, as measures against an ingredient (chemical use) such as urea, an increase in production of crude oil, and global warming, a method of removing and recovering CO2, which is contained in a flue gas, by bringing a flue gas of a boiler into contact with an amine-based CO2-absorbent and a method of storing recovered CO2 without releasing recovered CO2 to the atmosphere have been energetically studied for power generation facilities, such as thermoelectric power plants using a large amount of fossil fuel.
As a practical method of recovering and storing CO2 contained in a large amount of flue gas, there is a chemical absorption technique that brings a flue gas into contact with a CO2-absorbent such as an amine aqueous solution. A process for bringing a flue gas into contact with a CO2-absorbent in a CO2 absorber, a process for liberating CO2 and regenerating an absorbent by heating the absorbent having absorbed CO2 in an absorbent regenerator, and a process for circulating the absorbent in the CO2 absorber again to reuse the absorbent are employed as processes for removing and recovering CO2 from a flue gas by using the above-mentioned CO2-absorbent (Patent Literature 1).
The operation of a CO2 recovery apparatus using this chemical absorption technique in the related art causes an amine aqueous solution and CO2 to be separated from each other in the absorbent regenerator by high-temperature steam, but the consumption of this steam (energy) has needed to be minimized. For this purpose, methods using a mixture of two or more kinds of different CO2-absorbents (Patent Literatures 2 and 3) and a method of improving a process for feeding a CO2-absorbent (Patent Literature 4) have been examined until now.